glXCreateContext creates a GLX rendering context and returns
its handle. This context can be used to render into both windows and GLX
pixmaps. If glXCreateContext fails to create a rendering context, NULL is
returned.

If direct is True, then a direct rendering context is created
if the implementation supports direct rendering, if the connection is to
an X server that is local, and if a direct rendering context is available.
(An implementation may return an indirect context when direct is True).
If direct is False, then a rendering context that renders through the X
server is always created. Direct rendering provides a performance advantage
in some implementations. However, direct rendering contexts cannot be shared
outside a single process, and they may be unable to render to GLX pixmaps.

If shareList is not NULL, then all display-list indexes and definitions
are shared by context shareList and by the newly created context. An arbitrary
number of contexts can share a single display-list space. However, all rendering
contexts that share a single display-list space must themselves exist in
the same address space. Two rendering contexts share an address space if
both are nondirect using the same server, or if both are direct and owned
by a single process. Note that in the nondirect case, it is not necessary
for the calling threads to share an address space, only for their related
rendering contexts to share an address space.

If the GL version is 1.1 or
greater, then all texture objects except object 0, are shared by any
contexts that share display lists.

XVisualInfo is defined in Xutil.h.
It is a structure that includes visual, visualID, screen, and depth elements.

A process is a single execution environment, implemented in a single address
space, consisting of one or more threads.

A thread is one of a set of subprocesses
that share a single address space, but maintain separate program counters,
stack spaces, and other related global data. A thread that is the only member
of its subprocess group is equivalent to a process.

It may not be possible
to render to a GLX pixmap with a direct rendering context.